1. Field of the Invention
This invention relates to an electromagnetic inspecting apparatus which is suitable for electromagnetically detecting a defect present in a magnetizable wire rope used, for example, for the traction of an elevator cage in an elevator system or a cable car in a cable railway.
2. Description of the Prior Art
In a wire rope used generally for the traction of an elevator cage in an elevator system or a cable car in a cable railway, one or more of wires constituting the wire rope may be broken or locally worn during a long period of time of use, resulting in a gradual reduction of the residual mechanical strength of the wire rope. It is therefore a common practice to periodically inspect the wire rope for the presence of such a defect so as to replace the wire rope by a new one before a serious accident occurs.
While visual inspection was mostly resorted to in the past for the inspection of the presence or absence of a defect in such a rope, a method of magnetically inspecting such a rope for the presence or absence of a defect has recently been put into practice although such a manner of inspection has not yet been widely employed in this field. A known publication, for example, Japanese Utility Model Publication No. 2047/'75 discloses a detector for use in an electromagnetic inspecting apparatus for detecting a defect present in a steel wire rope. According to the disclosure of this known publication, a steel wire rope previously magnetized by an exciter or magnetizer is passed through the detector comprising a detecting coil which detects the intensity of leakage magnetic flux appearing when a defect is present in the steel wire rope. However, due to the fact that such a manner of inspection can detect merely the intensity of leakage flux, the proposed method has been defective in that the sensitivity of defect detection is considerably low, and there is also a great tendency of mixing of noise into the detector output signal, resulting in difficulty of ensuring the desired sufficient accuracy of defect detection.